For studying the properties of a plastic or elastic sample when subjected to mechanical processing, an apparatus is needed which makes it possible to carry out reproducible tests.
Present-day techniques comprise e.g. a masticating device as disclosed by Kleber et al. in Journal of Dental Research, 60 (1981):2, pp 109-114, which is used for in vitro assessment of the abrasive effects of chewing gum on teeth, and a measuring device as described by Christrup et al. in Arch. Pharm. Chem. Sci., 1986, 14, pp 30-36, which is used for in vitro measurements of the release of substances included in a chewing gum.
The prior art devices comprise two mutually reciprocatory jaws or pistons which are disposed in a container and between which the sample is to be processed.
The properties which may be of interest to determine thus are, inter alia, the action exerted by the sample on the pistons or some part thereof, the plasticity of the sample and/or the release of substances included in the sample to a liquid surrounding it, all as a function of the processing time and/or the processing technique. The purpose of the determination may be comparative, i.e. primarily for quality control, and/or imitative, e.g. with respect to in vivo processing by chewing.
A particularly interesting field for using such a mechanical processing apparatus is the processing of pharmaceutical preparations in the form of plastic samples, preferably chewing gums, in which case it should be possible in a reproducible manner to determine the period of time during which active substances in the sample are released to a liquid surrounding the sample.
In addition to the processing technique, the release of substances may be affected by the components included in the chewing gum, such as consistency agents, softeners, preservatives, gum bases, flavourings, as well as active substances in the form of drugs or nicotine, but also by the method of making the chewing gum. Further, the release is affected by the environment in which it takes place, i.e. the temperature and the composition of the liquid surrounding the sample, and the apparatus should be able to maintain at least the temperature constant.
One drawback of the prior art devices is the problem of cleaning the container or reservoir in which the sample is processed. The tendency of the sample to move or spread outside the processing area of the pistons or jaws has also been observed in the prior art devices. Another problem concerns the fact that the sample tends to adhere sometimes to one jaw, sometimes to the other and, above all, to separate parts floating freely in the liquid and escaping further processing.
In view of these problems, it is therefore very difficult to obtain an exact and reproducible processing of the samples by using the prior art devices. From this of course follows that it will not be possible to obtain reliable and reproducible release rates which can be used for scientific or manufacturing purposes.